When you're one of the top people in the Empire it means you're going to have to travel. Now when you're going from planet to planet it means you'll encounter different types of environments such as the icy cold on planet Hoth or the murky swamps of Dagobah. But when Darth Vader makes his way to his home planet of Tatooine he always makes sure he packs his light weight shirt with open backed mask. This is the only way he can keep comfortable while still being intimidating on a desert planet.